usb/host: introduce USB_ARCH_HAS_XHCI

to make it look like OHCI and EHCI, we introduce
that symbol and USB_XHCI_HCD depend on that
instead of PCI.

[bigeasy@linutronix.de: wire up USB_ARCH_HAS_HCD]

Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>